In power-actuated chucks, a rotationally symmetrical chuck body is mounted upon the head stock spindle of a machine tool and generally carries a plurality of (e.g. three or four) chuck jaws which are radially displaceable in respective guides inwardly and outwardly, respectively, to engage a workpiece or to disengage therefrom.
It has previously been recognized that rotation of the chuck body at high speeds tends to generate a centrifugal force at each jaw which urges the same outwardly and may relax the force with which the jaw engages the workpiece. For this reason chucks have been provided heretofore with counterweights on respective levers adapted to bear upon the jaw and thus apply a force which resists the centrifugal force on the jaws themselves.
Such a chuck has been described in German Open Application DT-OS No. 2,132,130. In this chuck, the centrifugal weights are received in recesses formed directly in the chuck body and on which the levers are swingable. Since each chuck jaw is generally provided with a respective centrifugal weight and lever, the levers are formed of the double-arm type with the weight being mounted upon the long lever arm and the short lever arm bearing directly against the chuck jaw. Such systems have several disadvantages.
The chuck body is subjected to excessive forces because, in addition to the centrifugal forces which are normally applied and which act upon the chuck jaws, the centrifugal forces applied to the weights eventually must be absorbed by the chuck body as well. Since the chuck body is provided with numerous additional recesses to accommodate the levers, counterweights and the like, these additional stresses have been found to create deformations which are highly undesirable, cause material fatigue and generally act to weaken the chuck and reduce the effectivity thereof.
In fact, when such chucks are operated at high speeds, structural failure of the chuck body poses a serious danger. The chuck body tends to lose its stiffness and tends to deteriorate.
These effects are all the more noticeable as the diameter of the chuck and the speed at which it is operated increase.